1. Field
Apparatuses consistent with the exemplary embodiments relate to an optical lens, and more particularly, to a fluidic lens.
2. Description of the Related Art
With the development of digital technology, digital convergence continues to increase. Digital convergence has occurred most in the fields of media and communication. An example of a product resulting from such digital convergence is a mobile communication device, in which an image pickup device such as a digital camera or a digital camcorder is coupled to the mobile communication device. In addition, such a mobile communication device can be coupled to an apparatus having functions including games, music playback, broadcast reception, and internet browsing. In general, other similar image pickup devices may be mounted on other types of mobile electronic devices such as laptop computers or personal digital assistants (PDA).
Such mobile electronic devices having an image pickup device have become increasingly compact and slim. Moreover, other digital electronic devices such as, for example, MP3 players, moving picture players or digital multimedia broadcasting (DMB) televisions, are commonly included in the mobile communication device in addition to the image pickup device. For this reason, demand for image pickup devices which are even more compact and slim is continually growing. However, such an image pickup device having focusing optics is one of the most difficult to downsize.
When image pickup apparatuses originally started to be combined with mobile electronic devices, there was not a high demand for high performance image pickup devices. However, in recent times, in order to satisfy growing user demands for mobile electronic devices having a high quality image pickup device, mobile electronic devices having an image pickup device have become diversified. For example, unlike the early days in which the limit of a close up function (provided by an image pickup device in a mobile electronic device) was 60 cm and a focal distance was fixed, in recent times, an auto-focusing function or a zoom function, and a shooting function at a close range below 30 cm have become desired by users to be provided in such an image pickup device.
In order to implement an auto-focusing function, a zoom function, and a close up function, a focal length of focusing optics needs to be adjusted. As an example of methods of varying a focal length in focusing optics, a step motor or a voice coil motor (VCM) may be used. In this case, the focal length is adjusted by varying a gap between lenses forming the focusing optics through a motor operation, thereby causing a size of the image pickup apparatus to be increased and consequently causing difficulty in mass production.
One method of overcoming such drawbacks resulting from the method using the step motor or VCM is to use a fluidic lens. The fluidic lens has a structure in which optical fluid is sealed by an optical membrane, and the curvature of the fluidic lens is adjusted by changing a pressure applied to a lens surface of the optical membrane by the optical fluid. As an example of such a fluidic lens, applicant of the instant application has filed “An optical lens and a method thereof,” Korean Unexamined Patent No. 2008-004316 which is incorporated herein by reference for all purposes.
Since the fluidic lens adjusts its focal length by use of the change in curvature of a lens surface, there is no need for the change in distance between lenses forming focusing optics to adjust the focal length. Accordingly, an image pickup apparatus including a fluidic lens does not need to be provided with a step motor or VCM to move the lenses forming the focusing optics and does not require an extra space set to move the lens, thereby ensuring a small structure. In addition, the fluidic lens disclosed in Korean Unexamined Patent No. 2008-004316 is more suitable for mass production, and requires less in manufacturing cost.
Meanwhile, most of the electronic equipment including mobile electronic equipment is designed to operate in a predetermined temperature range. The operation temperature of electronic equipment may vary depending on the intended use and functions of the electronic equipment, typically ranging from −20 to 60 degrees Celsius. The image pickup apparatus having a fluidic lens also operates in this range of operation temperature.
Optical fluid used in the fluidic lens has a higher thermal expansion coefficient than other components forming the fluidic lens, and causes higher change in volume according to temperature change. The focal distance of the fluidic lens is adjusted by the change in curvature of a lens surface. The curvature of a lens surface is changed by a pressure applied to an optical membrane by optical fluid. However, as noted above, the curvature of a lens surface may be changed according to temperature change, causing the focal distance to be changed. Such an unintended change of the focal distance may cause abnormal operation of the fluid lens in a predetermined temperature range (for example, ranging from −20 degrees to −60 degrees Celsius).